1. Field of the Invention
The invention relates generally to a hydrostatic transmission in a closed circuit with a hydraulic engine that is connected to a hydraulic pump. The stroke volume of at least the pump or the motor, and preferably the pump and the motor are regulated by feed pressure, and a flushing system is provided that includes a reversing valve connected to two pressure lines and controlled by the pressure prevailing in the lines. The reversing valve is connected to a delivery valve by the low-pressure line.
2. Description of Related Prior Art
This type of hydrostatic transmission is described in U.S. Pat. No. 3,846,982 wherein the stroke volume of the hydraulic pump is regulated by high pressure which is a disadvantage in a transmission of this type because high-pressure adjustment requires the absorption of large forces at the limit stops in the stroke-volume control. In addition, the large-pressure differential between the minimum high pressure and the maximum high pressure causes uneven control forces and control times. Another disadvantage of this type of hydrostatic transmission is that when two such hydrostatic transmissions are required, as in the case of crawler drives, different pressures may be produced by different tractional resistances on the opposite sides of the vehicle. This difference causes the stroke-volume controls of the hydraulic engines to be supplied with different control pressures which causes the stroke volumes and the driving speeds to differ on each side of the vehicle which results in deviations from the desired direction of travel unless constantly adjusted.
To avoid the above-noted problems, it is known to provide a low-pressure control instead of a high-pressure control. However, a low-pressure control requires a separate feed pump which increases the cost of the vehicle. In addition, low-pressure control has the disadvantage that large regulating pistons are necessary to produce a sufficient control force and the machine must be large.
The present invention avoids the above-mentioned disadvantages and provides a simple and economic hydrostatic transmission. The stroke-volume adjustment of at least one of the hydraulic machines is determined by the delivery pressure which is lower than the pressure in the high-pressure line.